The invention relates to an improvement in a hydraulic motor, having an inner-toothed toothed ring, an outer-toothed toothed wheel that rotates inside the toothed ring at a rotational speed and orbits therein at an orbital speed, a shaft, which is connected non-rotatably to the toothed wheel, with a suitable hydraulic fluid valve. Such a machine is known from U.S. Pat. No. 3,288,034.
Such a machine operates according to the gerotor principle. The toothed wheel generally has one tooth less than the toothed ring and is mounted eccentrically in the toothed ring. The geometries of the toothed wheel and toothed ring are so matched with one another that a number of pressure pockets are formed between the toothed wheel and the toothed ring. That number corresponds to the number of teeth of the toothed wheel. The individual pressure pockets are sealed of from one another by the points of contact between the toothed wheel and the toothed ring. On rotation of the toothed wheel, the toothed wheel orbits relative to the toothed ring by a number of revolutions that corresponds to the number of teeth of the toothed wheel. In the process, the pressure pockets in one half of the toothed gearing formed by the toothed ring and toothed wheel increase in size, whilst the pressure pockets in the other half of the toothed gearing decrease in size. The dividing line or plane between those two halves revolves at the orbital speed of the toothed wheel. In the case of the pressure pockets that are decreasing in size, care must be taken to ensure that the displaced fluid can escape. In the case of the pressure pockets that are increasing in size, care must accordingly be taken to ensure that fluid can be fed in. In a motor, fluid is supplied, under pressure, to the pressure pockets that are increasing in size, whilst in a pump the fluid from the pressure pockets that are decreasing in size is brought to a higher pressure. The valve arrangement is required to ensure correct supply to the individual pressure pockets. The valve arrangement must ensure that the connection between supply connections and the pressure pockets is always made at the right moment. This control of the hydraulic fluid, also called xe2x80x9ccommutatingxe2x80x9d, generally requires a valve arrangement of relatively complicated construction, which results in an increase in the volume and weight of the machine.
It is therefore an object of this invention to enable simplified construction of the valve arrangement in such a motor.
The instant invention has a valve arrangement including a rotary slide valve, which rests against an end face of a toothed wheel and rotates relative to the toothed ring at the orbital speed.
In that construction it is possible to provide the valve arrangement in the direct vicinity of the toothed gearing. This avoids the need for a separate xe2x80x9ccoverxe2x80x9d for the toothed gearing. It also makes it possible to avoid having two seals, namely on the one hand between the toothed gearing and the mentioned cover and on the other hand between the rotary slide valve and the cover on the opposite side. Although the rotary slide valve thus rests directly against the toothed wheel, it moves relative to the rotating toothed wheel at a speed determined by the ratio of the rotational speed to the orbital speed of the toothed wheel. The rotary slide valve also effects a corresponding movement relative to the toothed ring. This is not critical, however, because the rotary slide valve, owing to its relatively high rotational speed, can always ensure that its side to which fluid is supplied is connected to the pressure pockets that are increasing in size, whilst its other side, which is connected to a connection for escaping fluid, is connected to the pressure pockets that are decreasing in size. Accordingly, any leakages at the contact face between the rotary slide valve and the toothed wheel or the toothed ring are relatively uncritical. What is important, however, is that no short circuit occurs through the rotary slide valve or over it. As a result of the fact that the rotary slide valve is arranged directly at the toothed gearing, it is also possible to save a certain amount of constructional space, which additionally results in weight being saved, because fewer parts are required. The number of moving parts is kept extraordinarily low. In the valve arrangement, in principle only the rotary slide valve is moved. The orbital speed is the speed at which the centre points of the toothed wheel and toothed ring rotate relative to one another.
The rotary slide valve and the toothed wheel are preferably connected to one another directly by way of a drive connection. The direct connection of the toothed wheel and rotary slide valve reduces commutation faults, which could be caused by play. The commutation can accordingly be effected more precisely, so that noise is avoided and efficiency losses remain low.
Preferably the drive connection is formed by a pin that engages the toothed wheel centrally and the rotary slide valve eccentrically, which pin is mounted to rotate relative to at least one of the two parts, the rotary slide valve being mounted centrally in a valve housing. The pin that engages the rotary slide valve eccentrically thus forms a crank mechanism that converts the orbital movement of the toothed wheel into a rotational movement of the rotary slide valve. That crank mechanism is especially advantageous in a situation in which the rotary slide valve rests against the toothed wheel, because in that case there are no exposed lengths on which the pin could become bent. Very precise control of the rotary slide valve is thus obtained by the toothed wheel.
It is especially preferred for the pin to be formed integrally with one of the two parts, toothed wheel and rotary slide valve. xe2x80x9cIntegrallyxe2x80x9d should here be understood as meaning that the pin is secured firmly, that is to say without play, in the associated part. This can be achieved firstly by the pin actually forming a unit with the associated part. That integrality can also be obtained, however, by securing the pin to the part by a different method, for example by forcing into position, shrink-fitting, welding or similar methods. The possibility of play is then restricted to a single point of connection, namely at the point at which the pin cooperates with the other of the two parts.
It is especially preferred for the pin to be mounted rotatably in a bore, the inner diameter of which corresponds to the outer diameter of the pin. The diameter of the bore and pin can be matched with one another relatively precisely. The risk of play occurring is thus further reduced.
The rotary slide valve preferably divides the interior of the valve housing into a high-pressure side and a low-pressure side. As already explained above, this has the advantage that the dividing line between the high-pressure side and the low-pressure side rotates at the speed of the rotary slide valve. This corresponds to the orbital speed of the toothed wheel relative to the toothed ring. The individual pressure pockets between the toothed wheel and toothed ring are thus automatically exposed to the correct pressure distribution at their supply side.
Preferably pressure pockets formed between the toothed wheel and the toothed ring are open towards the interior. No additional channels are therefore required to supply the fluid to, or take it away from, the pressure pockets. This avoids pressure losses so that the efficiency of the machine can be improved further.
Preferably, in each case a sealing strip is arranged at the rotary slide valve between the high-pressure side and the low-pressure side, which sealing strip rests radially inwards against the valve housing. That sealing strip ensures that the rotary slide valve and the valve housing can also be formed with a small amount of play between them, that is to say the friction losses between the valve housing and the rotary slide valve are reduced because contact is restricted to the region of the sealing strip, which region is relatively small in the circumferential direction. The sealing strip, for its part, ensures sufficient separation between the high-pressure side and the low-pressure side, that sealing zone rotating with the rotary slide valve relative to the valve housing.
It is preferred for the sealing strip to be mounted with play relative to the rotary slide valve. That construction has the advantage that hydraulic fluid from the high-pressure side can pass underneath the sealing strip and thus provides contact pressure of the sealing strip against the inner circumference of the valve housing. The greater the pressure difference between the high-pressure side and the low-pressure side, the greater is the sealing requirement. That requirement is automatically fulfilled by the fact that the sealing strip in such a case is pressed against the inner circumference of the valve housing with increased pressure.
The rotary slide valve preferably has a first supply channel, which opens on one side of the rotary slide valve and passes through a bearing pin, and a second supply channel, which opens, on the one hand, on the other side of the rotary slide valve and, on the other hand, into an annular chamber surrounding the bearing pin. The rotary slide valve is thus additionally used to distribute the hydraulic fluid from a supply arrangement to the high-pressure side and the low-pressure side.
It is especially preferred for the bearing pin to be mounted rotatably in an end-face cover.
In an alternative construction, the rotary slide valve can have on its end face remote from the toothed wheel a high-pressure xe2x80x9ckidneyxe2x80x9d shaped recess and a low-pressure xe2x80x9ckidneyxe2x80x9d shaped recess, which, upon rotation, come into registration with openings of channels, the channels passing around the outside of the rotary slide valve to the end face of the toothed wheel. In that construction, the rotary slide valve itself can be of smaller construction, which is advantageous especially in the case of rapidly rotating machines, because the moment of inertia of the rotary slide valve is then smaller. That construction is not generally associated with an increase in constructional length because the channels can be formed in an end-face cover that is necessary anyway.